Status:Finalised Material from: Linus / Tim
Discussed in the following Daily reports:
http://intra.ecmwf.int/daily/d/dreport/2015/11/26/sc/
http://intra.ecmwf.int/daily/d/dreport/2015/11/30/sc/
1. Impact
A small but vicious frontal wave cyclone sped east across Scotland the N Sea on 29 November, and delivered extreme gusts to parts of Denmark and SW Sweden, with amber warnings in force in the affected areas, and red warnings in Germany. The storm system was also named "Nils II" by the Free University of Berlin, and "Clodagh" by Met Eirrean. Some damage and power outages also affected the UK and Ireland.
2. Description of the event
Infra-red imagery (above) and indeed several other aspects showed all the hallmarks of a sting jet, and it looks very probable that this was the cause of the narrow swathe of extreme gusts in the worst affected areas mentioned above. Indeed this and the general cyclone evolution seem to fit the conceptual picture and descriptions developed in this recent paper very well: http://www.tellusa.net/index.php/tellusa/article/view/27128
Satellite-images from 29 Nov 12z, 18z and 21z (from yr.no):
Radar images from 18z, 21z and 00z (30 Nov), from SMHI:
The plots below show wind observations from DMI and SMHI along a west-to-east line:
An animation of the interpolated wind gusts can be found here: http://www.smhi.se/klimatdata/meteorologi/vind/2.3355
Maximum wind gusts:
3. Predictability
3.1 Data assimilation
3.2 HRES
O-suite:
HRES 24-hour maximum wind gusts
E-suite:
HRES E-suite 24-hour maximum wind gusts
The plots below shows time-series of various variables from an e-suite experiment with output every time-step (7.5 min) for Karup, Denmark. The top plot includes the precipitation during the time-step *10 (blue), 10-metre mean wind (red), 10-metre wind gusts with convective contribution (purple) and without (pink). The bottom plot includes 2-metre temperature (blue) and 2-metre dew point (red). Please note that the wind gusts here includes the bug in the convective part and should be multiplied with 0.6.
3.3 ENS
EFI and SOT for wind gusts Sunday 29 November:
3.4 Monthly forecasts
3.5 Comparison with other centres
4. Experience from general performance/other cases
- On 4 December another suspected Sting Jet hit northern Danmark and western Sweden (Helga, http://www.smhi.se/klimatdata/meteorologi/vind/2.3359 ).
5. Good and bad aspects of the forecasts for the event
- Strong signal of a windy day a week in advance (EFI)
- The small-scale low visible in HRES 4 days before the event
- Suspicions of too strong wind gusts in e-suite. A bug was later found in the wind gust formulation and was corrected in the e-suite from 14 December 12z.